Fully-differential CMOS current-mode circuits and applications

A CMOS fully differential current-mode analog signal processing technique has been developed. The basic building block, a 5-V fully differential current-mode operational amplifier (I-OPAMP), has been integrated using the MOSIS 2 mu m n-well CMOS technology. Measured total harmonic distortion (THD) is -70 B with a peak signal (1) to a bias current (I) ratio of 0.5. By simply adding MOS switches, the I- OPAMP topology is easily extended to implement fully differential switched-current (SI) circuits with first-order cancellation of clock-feedthrough effects. A five-pole Chebyshev lowpass fully differential SI ladder filter has also been integrated in the 2 mu m p-well CMOS technology. Measured results show that with a sampling frequency of 128 kHz, the desired ripple bandwidth of 5 kHz is accurately realized using the fully differential SI structure.<
>